/*
 * Copyright 2018 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/*
 * The file lib_crc.c contains the  functions used for the calculation of
 * CRC-16 cyclic redundancy values.
 */

#include "lib_crc.h"

/*********************************************************************
 *                                                                   *
 *   Library         : lib_crc                                       *
 *   File            : lib_crc.c                                     *
 *   Author          : Lammert Bies  1999-2005                       *
 *   E-mail          : info@lammertbies.nl                           *
 *   Language        : ANSI C                                        *
 *                                                                   *
 *                                                                   *
 *   Description                                                     *
 *   ===========                                                     *
 *                                                                   *
 *   The file lib_crc.c contains the private  and  public  func-     *
 *   tions  used  for  the  calculation of CRC-16, CRC-CCITT and     *
 *   CRC-32 cyclic redundancy values.                                *
 *                                                                   *
 *                                                                   *
 *   Dependencies                                                    *
 *   ============                                                    *
 *                                                                   *
 *   lib_crc.h       CRC definitions and prototypes                  *
 *                                                                   *
 *                                                                   *
 *   Modification history                                            *
 *   ====================                                            *
 *                                                                   *
 *   Date        Version Comment                                     *
 *                                                                   *
 *   2005-05-14  1.12    Added CRC-CCITT with start value 0          *
 *                                                                   *
 *   2005-02-05  1.11    Fixed bug in CRC-DNP routine                *
 *                                                                   *
 *   2005-02-04  1.10    Added CRC-DNP routines                      *
 *                                                                   *
 *   1999-02-21  1.01    Added FALSE and TRUE mnemonics              *
 *                                                                   *
 *   1999-01-22  1.00    Initial source                              *
 *                                                                   *
 *********************************************************************
 */

/* CRC16 lookup table for polynom 0xA001 */
static const unsigned short crc16_tab[256] = {
	0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
	0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
	0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
	0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
	0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
	0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
	0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
	0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
	0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
	0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
	0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
	0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
	0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
	0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
	0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
	0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
	0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
	0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
	0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
	0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
	0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
	0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
	0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
	0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
	0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
	0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
	0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
	0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
	0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
	0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
	0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
	0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};

/*********************************************************************
 *                                                                   *
 *   unsigned short update_crc( unsigned long crc, unsigned char c ) *
 *                                                                   *
 *   The function update_crc calculates a  new  CRC-16  value        *
 *   based  on  the  previous value of the CRC and the next byte     *
 *   of the data to be checked.                                      *
 *                                                                   *
 *********************************************************************
 */
unsigned short update_crc(unsigned short crc, unsigned char c)
{
	unsigned short tmp;

	tmp = crc ^ (0x00ff & (unsigned short)c);
	crc = (crc >> 8) ^ crc16_tab[tmp & 0xff];

	return crc;
}
